Physics
drorzel | July 30, 2010Commenter miller asks:
It's often said that virtual particles can "borrow" energy, as long as it's for a short enough time to be compatible with the uncertainty principle. This never made sense to me, because the uncertainty principle says that product of uncertainty in energy and uncertainty in time is greater than h-bar over 2, not less than. Please explain.
The relevant equation is in the graphic at the top of this blog, just to the right of the title-- the one with ΔEΔt. It's easy to get turned around with this, due to the slightly unfamiliar business of working with inequalities.
The…
drorzel | July 30, 2010There's some good stuff in yesterday's post asking what physics you'd like to read more about. I'm nursing a sore neck and shoulder, so I'll only do one or two quick ones today, starting with James D. Miller in the first comment:
1) Is it true that our understanding of quantum physics comes from studying systems with only a small number of particles and there is a good chance our theories won't hold in more complex systems.
It all depends on how you define your terms-- what counts as a "small number" of particles, and what counts as not holding?
It's certainly true that most of the…
rallain | July 30, 2010The Lord of the Rings trilogy came on TV again recently. My wife and I can't help but to watch this even though we have it on DVD. Anyway, I was thinking about the part where Gondor sends a signal to Rohan asking them for military aid. Since this was before the invention of email, they had to do it with a signal fire. Hopefully this clip won't be a spoiler for you, but this is from the movie. Actually, all of the clips available have embedding disabled. So this is just a picture of that clip. If you want to see it, go to the youtube version.
One other spoiler: Sauron is really Frodo's…
drorzel | July 30, 2010The New York Times today has a story with the provocative title Getting Into Med School Without Hard Sciences, about a program at Mount Sinai that allows students to go to med school without taking the three things most dreaded by pre-meds: physics, organic chemistry, and the MCAT:
[I]t came as a total shock to Elizabeth Adler when she discovered, through a singer in her favorite a cappella group at Brown University, that one of the nation's top medical schools admits a small number of students every year who have skipped all three requirements.
Until then, despite being the daughter of a…
drorzel | July 29, 2010I was initially puzzled by the headline "Research-Assignment Handouts Give Students Meager Guidance, Survey Finds," and the opening sentences didn't help much:
Most research-assignment handouts given to undergraduates fail to guide the students toward a comprehensive strategy for completing the work, according to two researchers at the University of Washington who are studying how students conduct research and find information.
My initial reaction was "If I could give them a comprehensive strategy for completing the work, it wouldn't be research." Then I noticed the last three words, and…
drorzel | July 29, 2010I had intended to write up a recent paper for ResearchBlogging today, but I cleverly forgot to bring either the hard copy of the PDF home last night, which wrecked that plan. And I've got real lab work to do today, so it's not happening at work.
This seems like a good opportunity, though, to ask if there are things I ought to be explaining here that haven't occurred to me for one reason or another. So, as the post title says:
What topics in physics or related areas would you like me to write about here? This could be a recent paper, something from a recent news story ("I heard these guys in…
drorzel | July 29, 2010I'm going to be spending a good chunk of the rest of my day scrounging up adapters to connect two different classes of plumbing fittings. In honor of that, here's a poll question based on something that one research group used to do:
Sending a new graduate student to the lab down the hall to ask for a BNC to Swagelok adapter is:online surveys
Amusingly, I have seen something that easily could have been turned into a Swagelok to BNC adapter (in fact, I might still have one in my lab), that served a serious purpose.
(BNC is a type of electrical connection, Swagelok is a type of plumbing…
esiegel | July 28, 2010"`It's quite hard to destroy the Earth.'
Does that statement make anyone else nervous? I mean, does that sound like experience talking?"
-from the comments on the LHC at slashdot
Last week, I started an open thread, giving you the chance to ask about how certain we were about the validity of certain physical theories. (The thread is still open, FYI.) Here's the ranking scale I'm using, along with a few examples of where certain ideas currently fall.
And some of the most intriguing questions that came up were about the Higgs: what is it, how does it give mass to things, and is it even a…
drorzel | July 28, 2010Back at the start of the summer, I asked a question about automotive thermodynamics: On a hot day, is it better to open your car windows a crack when making a short stop, or leave them closed? For a long term-- say, leaving your car parked outside all day-- I hope everyone will agree that leaving the windows slightly open is the better call, but the answer isn't as clear for a short stop. There might well be some time during which the open-window car heats up faster as warm air from outside gets in, while the closed-window car holds in the air-conditioned goodness longer.
It occurred to me…
drorzel | July 28, 2010On Twitter, I saw Graham Farmelo link to this Physics World blog post about Ed Witten's Newton lecture, describing it as "Edward Witten's clearest-ever overview of string theory for laypeople (i.e. most others)." Witten's a name to conjure with, so I thought "That might be worth a look."
So I went to the blog post, which has video embeds for the two halves of the talk (~30 min each), each with a single frame frozen as an example. Both representative frames show slides that are nothing but words-- one full paragraph each, starting in the very upper left of the screen, and ending at the bottom…
drorzel | July 27, 2010When one of the most recent issues of Physical Review Letters hit my inbox, I immediately flagged these two papers as something to write up for ResearchBlogging. This I looked at the accompanying viewpoint in Physics, and discovered that Chris Westbrook already did most of the work for me. And, as a bonus, you can get free PDF's of the two articles from the Physics link, in case you want to follow along at home.
Since I spent a little time thinking about these already, though, and because it connects to the question of electron spin that I talked about yesterday, I think it's still worth…
drorzel | July 26, 2010The subject of the "spin" of the electron comes up again and again, so as pointed out in a comment, I really ought to do a post explaining what it is and how it works. As a bonus, this gives me the opportunity to do the dorkiest thing anyone has ever done with a cute-toddler video, namely this one:
(That's an early version of SteelyKid's new favorite game. I'll put a clip of the final version of the game at the end of this post.)
So, electron spin. Electrons, and all other fundamental particles, have a property known as "spin." This is an intrinsic angular momentum associated with the…
drorzel | July 25, 2010The vanity search this morning turned up something I hadn't seen before:
That's the Japanese edition of How to Teach Physics to Your Dog. I knew one was in the works, but hadn't heard when it would be out.
Of course, I can't read any of it other than my own name (rightmost column of the cover text, from top to bottom). So I turn to Google Translate, which does wonders with the product description:
Dogs have been collected by Professor Chad Emmy physics, quantum physics interested in all of the owner. Amazing ideas of quantum physics, every day, "honoring" significant useless wanted to apply…
drorzel | July 24, 2010Climate change is a major crisis, don't get me wrong, and it's something that needs to be discussed extensively in both scientific and policy circles. We're pumping carbon dioxide into the atmosphere at rather too high a rate, and getting something done about that is a key priority.
It's possible, though, to take the obsession on climate and CO_2 a little too far, though. Such as this news story from Physics World:
A cosmic gamma-ray burst striking the Earth could be harmful to ocean plankton at depths of up to 75 m, according to a team of Cuban researchers. These organisms account for up to…
drorzel | July 23, 2010Earlier this week, there was some interesting discussion of science communication in the UK branch of the science blogosphere. I found it via Alun Salt's "Moving beyond the 'One-dinosaur-fits-all' model of science communication" which is too good a phrase not to quote, and he spun off two posts from Alice Bell, at the Guardian blog and her own blog, and the proximate cause of all this is a dopey remark by a UK government official that has come in for some justifiable mockery.
Bell and Salt both focus on the narrowness of the "dinosaurs and space" approach-- a reasonably representative quote…
drorzel | July 23, 2010This week's big story in physics is this Science paper by a group out of Austria Canada (edited to fix my misreading of the author affiliations), on a triple-slit interference effect. This has drawn both the usual news stories and also some complaining about badly-worded news stories. So, what's the deal?
What did they do in this paper? The paper reports on an experiment in which they looked at the interference of light sent through a set of three small slits, and verified that the resulting pattern agrees with the predictions of the Born rule for quantum probabilities.
What does Matt Damon…
rallain | July 23, 2010Check this out - NY Times: No Motors, but Mistrust at Tour de France.
So, the short story is that some people claim that Cancellara is cheating by putting a hidden electric motor in his bike. Now they are going to do random hidden-motor checks.
I have analyzed this motor-in-a-bike already:
Energy in a hidden battery: The short answer is that you could get about 500 watts for about 1.5 hours with a hidden battery that weighs 1.6 kg. Doable, yes. Advisable? Probably not. Also, you would probably hear the motor being used.
Do bikers cheat? In this post I look at some clips of Cancellara…
drorzel | July 23, 2010The Dean Dad is worried about remedial math:
In a discussion this week with someone who spends most of her time working with students who are struggling mightily in developmental math, I heard an argument I hadn't given much thought previously: students who have passed algebra and even pre-calc in high school frequently crash and burn when they hit our developmental math, because the high schools let them use calculators and we don't.
[...][P]art of me wonders if we're sacrificing too much on the altar of pencil and paper. It's great to be able to do addition in your head and long division on…
drorzel | July 22, 2010Over at A Most Curious Planet, Alexandra Jellicoe offers a story with the provocative headline Is Science Sexist?, which spins off an anecdote from astronomy:
I was listening to Radio 4 a few months ago and the discussion about gender intelligence lodged in the deeper recesses of my brain unthought-of until recently when I went to see Jocelyn Bell Burnell talking of her 'Eureka' moment. She discovered the existence of neutron stars called Pulsar's in 1967 and I think she can safely be considered one of England's most pioneering and gifted scientists. I was struck by her comments that she…
ksnyder | July 22, 2010This is the first in an occassional series about Brookhaven's Relativistic Heavy Ion Collider, or, as it's affectionately called, RHIC.
Lil John has a theme song for RHIC's latest experimental run.
Sorry, sorry! I couldn't resist. RHIC's actual ditty of the moment goes more like this. (Clean version, of course, RHIC doesn't want any soap in its linac).
RHIC, which has a maximum potential energy of 200 billion electron volts (GeV), collided gold ions at energies as low as 7.7 GeV this spring -- the lowest ever achieved in the machine. But why go so low?
Even at low energies, the gold-gold…